Gas turbine buckets are often formed with a long, relatively thin shank which extends radially between the platform portion of the bucket and the dovetail base or root portion of the bucket. These shanks permit the use of a smaller diameter turbine wheel and attachment of the bucket dovetail base to the turbine wheel at a location of lower temperature. With such bucket construction, segmented coverplates are often employed on each axial side of the shanks to reduce gas flow leakage in the axial direction between the adjacent bucket shanks. Such coverplates are generally thin in axial thickness and may be attached to the turbine wheel at their radial inner ends and engage circumferentially extending clearance slots formed in the radially inner side of the bucket platforms. The turbine assembly usually includes an annular pin which seals the gap between adjacent bucket platforms and provides damping for the buckets. The pins are formed with notched ends and extend axially under the bucket platforms and are supported at each end by engagement of their notched ends with cutouts formed in the coverplates. A turbine assembly as generally described above is more fully shown in U.S. Pat. No. 3,137,478, issued June 16, 1964 and assigned to the assignee hereof. In such turbine assemblies, design considerations necessitate that the outer radial end of the thin coverplates remain in clearance with the bucket platform. Thus, even though the outer radial ends of the coverplates may extend into a platform slot or groove, they are free to vibrate. It has been found that the coverplates of such an arrangement may be susceptable to vibration and high cycle fatigue failure.
Accordingly a primary object of the present invention is to provide an arrangement for damping the outer radial ends of the coverplates of turbine assemblies or holding such ends against vibration.
A further object of the present invention is to provide a damping pin which will block leakage flow between adjacent bucket platforms and will be urged into frictional abutment with a coverplate by centrifugal force and damp coverplate vibration through the mechanism of heat producing relative slip or simply restrain the outer radial end of the coverplate so as to prevent vibration.